Effects Of Chlorine Disinfectants On The Microbial Community Structure And The Performance Of Anaerobic Digestion Of Swine Manure

The prevention and control of disease is a concern in pig farming.It is worth noting that African swine fever（ASF）is a new viral disease that has seriously threatened the global pig industry in recent years.Therefore,the use of various disinfectants to prevent epidemics is unavoidable.In recent years,China’s pig farms tend to be highly intensive and large-scale,greatly improving the efficiency of pig production.Highly intensive breeding pattern often requires more rigorous disinfection and precautions,which means more disinfection to be used.Therefore,residual disinfectant in pig manure is a noteworthy problem and should be paid close attention during the safe disposal of swine manure.In summary,in order to study the effect of residual chlorine disinfectant（CDs）on the anaerobic digestion（AD）of pig manure,sodium hypochlorite was selected as the representative of CDs.Firstly,the dose-effects of different concentrations of CDs（0,50,100,200 and 400mg/L）on methane yield and production rate were studied under mesophilic（35℃）and thermophilic（55℃）conditions,respectively.Then,the characteristics of digestive fluid were fully revealed.In addition,the shift of bacterial and archaeal communities was analyzed by 16 S r RNA gene pyrosequencing,and the linkages between the microbial community and the performance were connected.Finally,the effects of activated carbon（AC）,biochar（BC）and reduced iron powder（ZVI）on reducing the inhibition of CDs on anaerobic digestion were compared.This study contributes to a comprehensive understanding of the effects of hypochlorite disinfectant on anaerobic digestion,and provides effective strategies for alleviating the inhibitory effect of CDs on anaerobic digestion.The main results and conclusions obtained are as follows:（1）The effects of different doses of residual CDs on anaerobic digestion of pig manure were studied under mesophilic and thermophilic conditions.With the increase of CDs concentration,CDs inhibited methanogenesis at the initial stage of mesophilic anaerobic digestion,resulting in the delay time extended from 0.62 days to 0.85,1.9,3.8 and 5.5 days.Under thermophilic condition,the inhibition effect decreased significantly at the initial stage,but cumulative methane production（CMP）decreased at the later stage.（2）The feasible strategy of adding activated carbon（AC）,zero-valent iron（ZVI）and biochar（BC）to alleviate the inhibition of anaerobic digestion by CDs was explored at mesophilic condition.Further analysis showed that of all treatments,the AC group（M＿400AC）had the highest daily methane production rate（DMPR）(22.1,28.6,and 30.0 m L CH₄?g VS^-1?d^-1)on day 3,4,and 5 of digestion,significantly higher than the inhibitory group(2.7,7.4,and 14.4 m L CH₄?g VS^-1?d^-1).Therefore,AC should be preferred when the AD system is severely inhibited.（3）From the perspective of different CDs concentration and time evolution mechanism,the effects of disinfectants on the abundance,diversity,composition and difference of microbial communities in the mesophilic anaerobic digestion system of swine manure were elaborated and further discussed.The results showed that CDs lead to the selection of chlorine-resistant microbial communities.The relative abundance of sensitive bacteria and archaea（norank＿f＿SB-5 and Methanosaeta）decreased significantly.Clostridum＿sensu＿stricto＿1 and Methanosarcina dominated the resistant bacteria and archaea genera.